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It is distressing to carefully plant and care for squash plants only to watch them grow to produce fruit that turns black or brown on one end. A certain environmental disorder, blossom-end rot, appears as a brown or black spot on the blossom end of the fruit on squash and other garden plants. This preventable disorder leaves the fruit unsightly and renders them unusable.

About Blossom-End Rot

Blossom-end rot is not caused by a pathogen, which means that it is not a fungal or bacterial disease but rather an environmental disorder. This disorder appears first as small, light brown spots at the blossom end of the fruit. The spots enlarge and become sunken, leathery-looking, and brown or black. Hard brown areas may develop inside squash fruit. Blossom-end rot is caused by a calcium deficiency. Calcium is necessary for normal cell growth in developing fruits. Even where there is adequate calcium in the soil, excessive soil moisture fluctuations, drought conditions and excessive nitrogen can influence a squash plant's calcium uptake.

Site Preparation

Having the soil in your garden tested every few years is a good idea and will reveal any nutritional deficiencies in the soil and guide your selections of soil amendments and fertilizer. The recommended pH range for squash is 5.8 to 6.5. Unless a soil test recommends otherwise, plan to work a 5-10-10 fertilizer into the soil at a rate of 3 pounds per 100 square feet. Also work about 2 to 3 inches of an organic-matter soil amendment, such as well-rotted compost or aged manure, into the top 6 to 8 inches of soil. This is particularly important in sandy soils.

Care Practices

Spread an organic material mulch, such as shredded leaves or well-rotted compost, around the squash in a loose layer 2 to 4 inches thick. This will help to minimize fluctuations in soil moisture and encourage squash roots to efficiently take up calcium. The mulch will also suppress weeds and regulate soil temperature. Be careful when weeding around the squash plants, removing weeds by hand rather than with a hoe when they are near the base of a squash plant. Maintain even moisture around the squash roots, wetting the soil to a depth of 6 inches whenever soil about 1 inch below the surface feels dry to the touch. Ammonium inhibits calcium uptake, so avoid fertilizers that offer nitrogen in this form. Also avoid excessive applications of other nitrogen fertilizers or potash, especially when fruits are developing. Consider side-dressing squash plants with 2 pounds of calcium nitrate per 100 feet of row before vines start to develop.

Possible Fungal Diseases

Although a browning or blackening of just the blossom end of squash fruits typically indicates blossom-end rot, these plants are also prone to various fungal diseases that can cause a dark rot on fruit. Unlike with blossom-end rot, if the squash fruits are affected by a fungus, the rot is usually soft, not contained to just the blossom end and a fuzzy or powdery growth may eventually develop on affected areas. Some opportunistic pathogens may invade fruits already affected by blossom-end rot, making a positive diagnosis more challenging. Damp, crowded growing conditions, overhead irrigation or other splashing water and poor sanitation can encourage fungal diseases.

About the Author

Angela Ryczkowski is a professional writer who has served as a greenhouse manager and certified wildland firefighter. She holds a Bachelor of Arts in urban and regional studies.

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Hemera Technologies/Photos.com/Getty Images

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Ryczkowski, Angela. "Growing Squash in the Garden Without the End Turning Black." Home Guides | SF Gate, http://homeguides.sfgate.com/growing-squash-garden-end-turning-black-75315.html. Accessed 25 May 2019.

Ryczkowski, Angela. (n.d.). Growing Squash in the Garden Without the End Turning Black. Home Guides | SF Gate. Retrieved from http://homeguides.sfgate.com/growing-squash-garden-end-turning-black-75315.html

Ryczkowski, Angela. "Growing Squash in the Garden Without the End Turning Black" accessed May 25, 2019. http://homeguides.sfgate.com/growing-squash-garden-end-turning-black-75315.html

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